4. Acquisition

Time requirement: 30 min

Sample: 100 mg cholesteryl acetate in CDCl₃.

Load standard ¹³C NMR parameters and the DEPT pulse program. You have to set:

decoupler attenuation for hard decoupler pulses
td	64 k
sw	200 ppm
o1	middle of ¹³C NMR spectrum
o2	middle of ¹H NMR spectrum
p1	90° ¹H decoupler pulse
p2	180° ¹H decoupler pulse
p3	135° ¹H decoupler pulse
p4	90° ¹³C transmitter pulse
p5	180° ¹³C transmitter pulse
d1	2 s
d2	1/[2¹J(C,H)] = 3.5 ms, calculated from ¹J(C,H) = 140 Hz
decoupler attenuation and 90° pulse for CPD
ns	512

5. Processing

Use standard 1D processing as described in Experiment 3.2. Adjust the phase for the TMS signal positive.

6. Result

The figure shows the ¹³C DEPT-135 spectrum of cholesteryl acetate obtained on an AM-400 spectrometer. Note that no signals of quaternary carbon atoms appear. This is a disadvantage in comparison with the APT or PENDANT sequences. Compare the signal-to-noise ratio with that of Experiment 6.4, which was obtained under otherwise identical conditions. Note that for good DEPT results inverse probe-heads are unsuitable due to the coil geometry of both r. f. coils.

7. Comments

For the product operator formalism we consider a C,H spin pair and neglect the effects of chemical shifts, since these are refocused by the 180° pulses. The first 90° proton pulse creates transverse magnetization of the protons, which develops C,H spin coupling during the delay d2. If the delay τ is set equal to d2 = 1/[2¹J(C,H)] the cosine term becomes zero and the sine term unity, leaving pure antiphase magnetization of the proton with respect to carbon in the equation. This antiphase magnetization is converted